The present invention relates to a hydraulic shock absorber with an automatic vehicle height adjusting mechanism that is installed in a suspension system of a vehicle such as an automobile.
In general, vehicles such as automobiles have a hydraulic shock absorber installed between sprung and unsprung members of a suspension system to damp vibrations of the sprung and unsprung members, thereby improving ride quality and steering stability. However, vehicles having relatively large carrying capacities, e.g. vans and wagons, may be degraded in ride quality and steering stability by a large change in vehicle height due to a change in the carrying load resulting from the occupant getting on or off the vehicle, baggage loading or unloading, and so forth. Further, if the rear wheel-side vehicle height is lowered (rear sagging) by the load carried on the vehicle, the optical axis of the headlight is undesirably directed upward. Accordingly, there has been a demand for a suspension system capable of automatically keeping a constant vehicle height independently of the size of the carrying load.
Under these circumstances, Japanese Patent Application Laid-Open Publication No. Hei 9-144801, for example, proposes a self-leveling hydraulic shock absorber having a pump mechanism that supplies a hydraulic fluid from a hydraulic fluid tank into a cylinder by extension and contraction of a piston rod, and a return mechanism that returns the hydraulic fluid from the pump mechanism and the cylinder to the hydraulic fluid tank according to the extension-contraction position of the piston rod. By utilizing vibrations of the suspension system during running of the vehicle, the pump mechanism and the return mechanism are operated to control the pressure in the cylinder properly to adjust the extending length of the piston rod at a constant level, thereby automatically keeping a constant standard vehicle height.
Further, in the self-leveling hydraulic shock absorber disclosed in Japanese Patent Application Laid-Open Publication No. Hei 9-144801, the hydraulic fluid tank has a hydraulic fluid chamber and a gas chamber isolated from each other by a bladder (flexible diaphragm), thereby reducing the size of the tank in the height direction while surely preventing the gas from mixing into the hydraulic fluid. The hydraulic fluid tank is provided around the outer periphery of an outer tube (casing) below a suspension spring, thereby allowing the necessary volumetric capacity to be ensured by utilizing dead space.
The self-leveling hydraulic shock absorber disclosed in Japanese Patent Application Laid-Open Publication No. Hei 9-144801 suffers, however, from the following problems. When the hydraulic fluid tank is formed, annular members for retaining the bladder, which divides the gas chamber and the hydraulic fluid chamber, are secured to the outer tube by welding. Therefore, sputtering occurring during welding may cause contamination of the hydraulic fluid. In addition, heat of welding may deform the annular members, resulting in degradation of sealing performance.